A crane is a gravity working machine, a hydraulic actuator of the crane producing a large amount of energy in a lowering or braking process, for example, existing crane products usually producing a large amount of gravitational potential energy in winching and derricking lowering processes.
In the related art, in the winching and derricking lowering processes, the speed of winching and derricking lowering is adjusted by controlling the area of an orifice of a balance valve, such that all the energy generated in a lowering process of a load is converted into thermal energy, resulting in a waste of energy and a rise of the hydraulic oil temperature and reducing reliability of hydraulic components. Moreover, in order to reduce the rise of oil temperature, it is also necessary to increase the heat dissipated power of a radiator, causing an increase in the cost of design.